A:Answer It's never a set rule, but my experience in the past has been this:
If it's listed as "sold out online", it's rather temporary - maybe 1-2 weeks. However, if it gets the the point of "backordered", it could be 3-5 weeks. I have noticed a lot of great lenses will disappear entirely from the site too - sometimes they come back in a few months, or sometimes they never come back. I would guess in this case you have 1-2 weeks.
You can go in store and see if someone can check their ability to order the lens in store too. In rare cases, I have been able to order a lens in store that was listed as sold out online.